CN113785250A

CN113785250A - Calibration method and method for obtaining workpiece information

Info

Publication number: CN113785250A
Application number: CN202080031827.2A
Authority: CN
Inventors: 保罗·马克斯特德; 詹姆斯·亚瑟·哈特利
Original assignee: Renishaw PLC
Current assignee: Renishaw PLC
Priority date: 2019-03-27
Filing date: 2020-03-11
Publication date: 2021-12-10
Also published as: US20220184765A1; JP2022528842A; WO2020193944A1; EP3948453A1; EP3715977A1; US11794299B2

Abstract

A method, comprising: a) causing a tool mounted on a machine tool to process a workpiece, and at least one sensor configured to measure one or more aspects of the tool and/or machine tool to collect sensor data during said processing; b) the measuring device inspects the portion of the workpiece processed in step a) to obtain measurement data; and c) calculating sensor-to-workpiece data calibration information based on the sensor data and the measurement data.

Description

Calibration method and method for obtaining workpiece information

The present invention relates to obtaining calibration information for sensors configured to monitor aspects of a machine and/or tool during tool processing, so that information about a workpiece processed by the tool mounted on the machine tool can be inferred from data obtained by the sensors.

It is known to embed sensors in the body of the tool, in close proximity to the tool body, tool insert or cutting edge; for example, for monitoring properties/aspects of the tool or cutting process, such as deflection, temperature, load and/or vibration, during machining of a workpiece by the tool. Such tools are known in the industry as "smart tools". It is also known to embed sensors in parts of the machine tool, such as the spindle, for monitoring aspects of the machine tool during machining operations. The outputs of these sensors may be monitored to assist in tool setting, to assess whether a problem exists with the machining operation and to take action (e.g., stop the machining operation if the sensor outputs indicate an adverse condition), and also to attempt to provide some general prediction of the surface finish of the workpiece.

The present invention relates to a method of using such data in a new way so that the measurement data of the processed part (e.g. surface) of the workpiece can be inferred from the sensors. In particular, as described in more detail below, the method may include determining calibration information, for example relating measurement data regarding a portion of a workpiece being processed by the tool (measurement data obtained by inspection of the portion of the workpiece by a measurement device) to sensor data obtained while the tool is processing the portion of the workpiece. Such calibration information may then be subsequently used to infer measurement data about the processed portion of the workpiece from such sensor data obtained during other (e.g., subsequent) machining steps/operations.

According to a first aspect of the invention, there is provided a method comprising: a) causing a tool mounted on a machine tool to process (in other words, "machine") a workpiece, and at least one sensor configured to measure (e.g., monitor) one or more aspects/properties of the tool and/or machine tool, to collect sensor data during said processing ("machining"); b) the measuring device inspects the part of the workpiece that was processed ("machined") in step a) to obtain measurement data; and c) calculating sensor-to-workpiece data calibration information based on the sensor data and the measurement data.

A benefit of the present invention is that sensor-to-workpiece data calibration information ("calibration information") can be used to (automatically) infer information (e.g., measurement data) of portions of a workpiece that are processed (e.g., machined) at different (e.g., subsequent or earlier) times from sensor data obtained during such processing/machining. Accordingly, in other words, step c) may be said to determine "sensor data to workpiece data conversion information" (instead of "sensor to workpiece data calibration information"). Alternatively, the sensor-to-workpiece data calibration information may be referred to simply as "sensor calibration information". This may provide a number of different advantages. This may, for example, significantly reduce production cycle time. For example, rather than directly measuring all relevant aspects of a workpiece being processed by a smart tool using a dedicated measurement tool (such as a contact measurement probe), with the present invention, information may be calibrated using sensors to workpiece data, with high confidence that information (e.g. measurement data) about the workpiece is inferred from the sensor data obtained by sensors configured to measure (e.g. monitor) one or more aspects of the tool and/or machine tool during processing of the workpiece. In other words, inferred information (e.g., measurement data) about the workpiece from the sensor data may be used/output as actual information (e.g., measurement data) obtained by inspecting the processed portion of the workpiece with a dedicated measurement probe. This can save a significant amount of time, particularly when making a series of nominally identical articles. For example, using sensor-to-workpiece data calibration information obtained by measuring only some or even only one workpiece, information for an entire series of nominally identical workpieces can be inferred from sensor data obtained during workpiece processing/machining.

Further, sensor-to-workpiece data calibration information may be used to infer information about portions of a workpiece that are difficult or impossible to measure directly using a dedicated measurement device. For example, it may be difficult to accurately measure directly the features located towards the distal end of the elongated hole. For example, some holes may be many meters deep (e.g., at least 1m (meter), such as at least 2m, and such as at least 3m), and difficult to access the bottom end of the hole. Accordingly, the present invention may be used to infer measurement information about these features from sensor data obtained during processing of these features.

In other words, the method may include calibrating information to the workpiece data using the sensors, inferring information (e.g., measurement data) about different portions of the workpiece from sensor data obtained during processing of the different portions (by at least one sensor configured to measure one or more aspects of the tool and/or machine tool). The different portion may be located towards the bottom end of the bore, for example towards the closed end of the bore. The holes may be at least 2m long (or "deep"), for example, at least 3m long. The method may include inferring information for a portion of the hole located at least 1m from the first end of the hole (e.g., the open end, or the end where the hole is machined) using the sensor to calibrate the information for the workpiece data, optionally at least 1.5m from the first end of the hole, e.g., at least 2m or even 3m from the first end of the hole.

The length of the tool (e.g., the distance between i) the point at which the tool is retained in the toolholder and ii) the tool insert) may be at least 1m, such as at least 2m, such as at least 3 m. The method may include inferring information (e.g., measurement data) about a workpiece (e.g., the same or nominally the same workpiece) from sensor-to-workpiece data calibration information and sensor data relating to one or more aspects/properties of a tool and/or machine tool collected during workpiece processing (via at least one sensor configured to measure one or more aspects of the tool and/or machine tool). As described above, the present invention may be particularly advantageous when a workpiece is processed ("machined") by a long tool because the features formed by the long tool may be difficult to access by the measuring device.

As will be appreciated, step c) may calculate sensor-to-workpiece data calibration information from sets of sensor data and measurement data (e.g., from multiple different executions or repetitions of steps a) and b)) that may or may not be obtained from the same workpiece. For example, calibration information may be obtained from sensor data and measurement data obtained from performing multiple (e.g., the same) machining operations on the same workpiece, and/or from performing (e.g., the same) machining operations on different workpieces.

As will be appreciated, the method may include first performing steps a) to c), then performing a subsequent treatment (machining) of the workpiece, then inferring information about at least a portion of the subsequent treatment of the workpiece using the sensor-to-workpiece data calibration information and sensor data relating to one or more aspects/properties of the tool and/or machine tool collected during the subsequent workpiece treatment (by at least one sensor configured to measure one or more aspects of the tool and/or machine tool). Optionally, the method comprises performing a plurality of machining operations on a workpiece (or a plurality of nominally identical workpieces), then measuring only one machined portion (or only some of the plurality of portions) (or for example only one of the workpieces), thereby determining calibration information, and then using the calibration information to infer information about the other machined portions of the workpiece (or about the other workpieces). Accordingly, for example, it is not necessary to determine calibration information prior to processing/machining the portion to be subject to information inference.

The tool, machine tool and/or sensor used during processing of the workpiece from which information (e.g. measurement data) is inferred may be the same as the tool, machine tool and/or sensor used during step a). Of course, it may be assumed that for workpieces processed by nominally identical tools and machine tools, the same sensor-to-workpiece data calibration information may be used, with information (e.g., measurement data) inferred from sensor data obtained by nominally identical sensors. As will be appreciated, nominally identical sensors, tools and machine tools may be those having substantially the same specifications (e.g. configured to have the same performance/function and formed of substantially the same components). For example, nominally identical may mean that they originate from the same manufacturer and have the same model/part number. Accordingly, for example, if the tool is replaced by a (nominally) identical tool, the need to repeat steps a), b) and c) may be avoided. However, it may be preferred to repeat steps a), b) and c) even if the tool is replaced by a (nominally) identical tool, and/or even if the tool or the nominally identical tool is used to machine a nominally identical workpiece on a different machine tool. Such repetition of steps a) to c) may help to provide the most accurate inferred information (e.g., measurement data). Accordingly, the method may include repeating steps a) through c) with a tool or a portion thereof (e.g., a tool insert) replaced.

Optionally, steps a) to c) are repeated even if the tool is not changed/replaced. For example, steps a) to c) may be repeated at regular time intervals and/or predetermined time intervals. For example, steps a) through c) may be repeated after a predetermined amount of time (e.g., machining time with the tool) and/or after a predetermined number of machining operations are performed with the tool).

Optionally, repeating steps a) through c) if a significant change in environmental factor is detected. For example, the method may comprise repeating steps a) to c) if the temperature variation of the operating environment exceeds a predetermined threshold.

The workpiece of step a) may be one of a series of nominally identical workpieces to be processed (e.g. to form a series of nominally identical articles). Accordingly, for at least one other workpiece in the series, information regarding it may be inferred from sensor-to-workpiece data calibration information and sensor data obtained during processing thereof. For example, the method may further comprise processing a series of nominally identical workpieces to form a series of nominally identical articles (e.g., which are nominally identical to the workpieces/articles of step a). For at least some of the workpieces, information (e.g., measured data) may be inferred from sensor-to-workpiece data calibration information and sensor data relating to one or more aspects/properties of the tool and/or machine tool obtained during workpiece processing (via at least one sensor configured to measure one or more aspects of the tool and/or machine tool).

For example, the method may include: d) treating the same or nominally the same workpiece as in step a). Such a treatment can be carried out using the same or nominally the same tool, and/or the same or nominally the same machine tool, as used in step a). The method can comprise the following steps: e) information (e.g., measurement data) about the workpiece is inferred using sensor-to-workpiece data calibration information from sensor data collected during the process by (e.g., the same or nominally the same) sensors configured to measure one or more aspects of the tool and/or machine tool. Step d) may be performed after or before step b) and/or step c).

As will be appreciated, the nominally identical workpiece may be a workpiece comprising the same material as the workpiece of step a). The nominally identical workpiece may be a workpiece having substantially the same dimensions as the workpiece of step a). Nominally identical workpieces may be workpieces formed or to be formed to the same design specifications, such as the same Computer Aided Design (CAD) specifications. For example, the nominally identical workpiece may be a workpiece machined or to be machined according to the same machining instructions as the workpiece of step a).

The inferred information may include measurement data (e.g., absolute/quantitative) measurement data. For example, the measurement data may include a size measurement, such as an aperture. The measurement data may include error measurements. The measurement data may include surface roughness and/or surface waviness measurement data.

Optionally, the inferred information may include information regarding whether the processed portion of the workpiece is acceptable, such as whether a predetermined tolerance is met. For example, rather than determining absolute measurement data regarding surface roughness, the method may include using the sensor to workpiece data calibration information and sensor data obtained by at least one sensor (configured to measure/monitor one or more aspects/properties of the tool and/or machine tool) to make decisions regarding the workpiece and/or subsequent machining operations during (e.g., subsequent) machining of the workpiece. For example, sensor-to-workpiece data calibration information and such sensor data may be used to automatically determine whether a machining process of a workpiece (e.g., a workpiece or a nominally identical workpiece) is proceeding correctly and/or whether portions of the workpiece may be out of tolerance. This information may be used as part of an automatic feedback control loop, for example, to allow adjustments to be made to the machining of a workpiece in real time, and/or to allow adjustments to be made to subsequent machining steps of the same or nominally the same workpiece. This may be based on a threshold value generated/determined from sensor-to-workpiece data calibration information, for example.

The tool may comprise a fixed tool or a moving (e.g. rotating) tool. For example, the tool may be at least one of: boring bar, milling cutter, grinding cutter, reaming cutter, polishing cutter, or drilling cutter.

As will be appreciated, the calibration information may include functions, models, look-up tables, and/or data. As explained above, the sensor-to-workpiece data calibration information may be referred to as sensor-to-workpiece data conversion information (or just sensor calibration information).

The aspect/property of the tool and/or machine tool may comprise (in other words, the sensor data may comprise) at least one of: vibration, deflection, temperature, and/or load.

Accordingly, the at least one sensor may include any sensor configured to measure at least one of vibration, deflection, temperature, and/or load. For example, the at least one sensor may comprise at least one of: an accelerometer, a temperature sensor, and/or a strain gauge (e.g., a force sensor).

The measurement data and/or inferred measurement data may include at least one of: position, size, surface roughness, surface waviness of the workpiece.

Treating (in other words "machining") the workpiece may include at least one of: cutting, drilling, grinding, polishing, turning, reaming and milling.

The machine tool may comprise at least one sensor. For example, the tool holder and/or spindle of the machine tool may include at least one sensor. Advantageously, the tool may comprise at least one sensor. This may provide more accurate and repeatable sensor data. The tool may include a tool insert (or cutting edge) configured to interact with the workpiece to process the workpiece. The tool may include a tool body for holding a tool insert. Accordingly, the cutter insert may be mounted to the machine tool via the cutter body. The tool body may comprise at least one sensor. Preferably, the at least one sensor is located towards an end of the tool body proximate to the tool insert.

Step b) may be performed by a measuring device mounted on the machine tool. Optionally, step b) is performed by a measuring device mounted on a different positioning apparatus, for example on a Coordinate Measuring Machine (CMM).

The measurement device may comprise a measurement probe. The probe may be configured to measure dimensional attributes of the workpiece. For example, the probe may be configured to measure the position (e.g., coordinates) of a particular point in a three-dimensional measurement volume. Optionally, the probe is configured to measure the surface roughness and/or waviness of the surface. The measurement probe may comprise a contact measurement probe. The probe may comprise a deflectable stylus. The probe may be configured to determine and output the degree of deflection of the stylus. Such probes are commonly referred to as scanning probes or analogue probes. Such probes are distinguished from touch trigger probes which are configured to provide a "trigger" signal in response to stylus deflection exceeding a certain/threshold amount. As will be appreciated, the measuring device is separate from the tool. Accordingly, the method may include changing tools and measuring devices (e.g., automatically from a storage rack/carousel) onto and/or off of the tool holder. This may be particularly the case if the machine tool has only one tool holder.

The method may further include using the inferred information (e.g., measurement data). This may include using the inferred information (e.g., measurement data) to adjust subsequent processing of the workpiece or a subsequent nominally identical workpiece. Such adjustment may include using the inferred information (e.g., metrology data) to automatically adjust subsequent processing of the workpiece or subsequent nominally identical workpieces.

Step c) may include adjusting previously determined sensor-to-workpiece data calibration information (e.g., to make it specific to the current workpiece/series of workpieces, and/or to compensate for changes in the tool, machine tool, and/or operating environment) based on the sensor data and measurement data. For example, such adjustments may include offsetting previously determined sensor-to-workpiece data calibration information. Such previously determined sensor-to-workpiece data calibration information may be generic sensor-to-workpiece data calibration information, e.g., generic to the tool (and optionally the machine tool, e.g., tool/machine tool combination), but not specific to the workpiece. Accordingly, step c) may comprise adjusting/updating the general sensor-to-workpiece data calibration information (based on sensor data and measurement data) to determine sensor-to-workpiece data calibration information specific/specific to a particular workpiece, tool and machine tool combination. Accordingly, the method may comprise determining generic sensor-to-workpiece data calibration information for a particular tool (and optionally machine tool) combination, and then performing steps a) to c) in order to update/adjust the generic calibration information.

Step a) may comprise causing the tool to treat the workpiece in such a way that the tool experiences different machining properties (e.g. different loads, different amounts of vibration) at different points in space and/or time. Step b) may comprise the measuring device inspecting the portion(s) of the workpiece that have been subjected to such different machining properties. Accordingly, step c) may comprise calculating sensor-to-workpiece data calibration information from sensor data and measurement data associated with different machining properties.

In other words, step a) may comprise i) causing a tool mounted on the machine tool to process the workpiece according to a first machining parameter and collecting sensor data obtained by the at least one sensor during said processing according to the first machining parameter, and ii) causing the tool mounted on the machine tool to process the workpiece according to a second machining parameter (different from the first machining parameter) and collecting sensor data obtained by the at least one sensor during said processing according to the second machining parameter. The first and second machining parameters may be configured differently such that the tool experiences different properties (e.g., different loads, different amounts of vibration) during workpiece processing. Step b) may comprise inspecting (e.g. by at least one measuring device) the part/surface of the workpiece that has been formed by step i) and step ii). Step c) may include calculating sensor-to-workpiece data calibration information from the sensor data obtained at steps i) and ii) and the measurement data obtained at step b). As will be appreciated, step b) may be performed once after both steps i) and ii) have been performed (in which case steps i) and ii) may be performed at different locations on the workpiece). Alternatively, steps i) and ii) may be performed on the same portion of the workpiece, wherein step b) is performed after step i) and before step ii) to inspect the portion/surface of the workpiece formed by step i), and then step b) is repeated again after step ii) to inspect the portion/surface of the workpiece formed by step ii).

The sensor-to-workpiece data calibration information may be workpiece specific. In other words, sensor-to-workpiece data calibration information may be determined for the workpiece processed at step a), and for nominally identical workpieces (i.e., workpieces in a series of nominally identical workpieces). Accordingly, different sensor calibration information may be determined for different/non-nominally identical workpieces. Sensor-to-workpiece data calibration information may be determined for (e.g., may be specific to) a particular tool and machine tool combination. In particular, sensor-to-workpiece data calibration information may be determined for (e.g., may be specific to) a particular workpiece, tool, and machine tool combination.

The present application describes a method of inferring information about a workpiece being processed by a tool mounted on a machine tool apparatus from sensor data relating to one or more aspects/properties of the machine tool and/or the tool mounted thereon. The method may comprise (in any suitable order): a) determining sensor calibration information according to: i) actual measurement data of a portion of the workpiece that has been processed by the tool, and ii) sensor data relating to one or more properties of the machine tool and/or the tool mounted thereon obtained during processing of the portion measured in i) by the tool. The method may further comprise: b) sensor data relating to one or more properties of a machine tool and/or a tool mounted thereon obtained while processing a workpiece by the tool mounted thereon is acquired. The method may further comprise: c) using the sensor calibration information, inferred information (e.g., measurement data) about the workpiece is obtained from the sensor data obtained during step b).

According to another aspect of the invention there is provided a method of inferring measurement data relating to a workpiece being processed by a tool mounted on a machine tool, the method comprising, in any suitable order: a) obtaining sensor data obtained by at least one sensor configured to measure one or more aspects of the tool and/or machine tool as the tool processes the workpiece; and b) inferring information about the workpiece from the sensor data using sensor calibration information configured for a particular tool and workpiece combination.

As will be appreciated, any of the above methods may be computer-implemented. Accordingly, according to another aspect of the present invention, there is provided a computer program product comprising computer program code which, when executed by a computer, causes the computer to perform any of the methods described above. According to another aspect of the invention, a computer readable medium is provided, carrying computer program code as described above.

According to another aspect of the invention, there is provided a machine tool apparatus comprising a tool for processing a workpiece, at least one sensor configured to measure one or more aspects of the tool and/or machine tool during said processing of the workpiece, and a controller configured to cause (e.g. using computer program code) the machine tool apparatus to perform any of the above methods.

Embodiments of the invention will now be described, by way of example only, with reference to the following drawings, in which:

fig. 1 schematically shows a machine tool apparatus on which a tool for processing a workpiece is mounted;

figure 2 schematically illustrates the machine tool apparatus of figure 1 but with a measurement probe mounted on the machine tool in place of the tool;

FIG. 3 is a flow chart of an example process according to the present invention; and

fig. 4a to 4c are graphs illustrating possible calibration models.

Referring to fig. 1, there is shown a machine tool apparatus 2 comprising a machine tool 4, a numerical controller 6(NC) (e.g. a computer numerical controller or "CNC"), a PC 8 and a transmitter/receiver interface 10. Machine tool 4 includes a tool holder 12 that holds and moves a tool 20 relative to a workpiece 16 mounted in a spindle 18. The NC 6 controls the rotation of the spindle 18 and the x, y, z movement of the toolholder 12 within the working area of the machine tool using motors and encoders (not shown) and the like. The NC 6 may be programmed to machine operations, for example, via the PC 8.

In the depicted embodiment, the tool 20 is a boring bar and includes a tool body 22 and a tool insert 24 (such as a cutting insert configured to interact (e.g., cut) with a workpiece to machine the workpiece. the boring bar 20 (particularly the tool body 22) includes at least one sensor 26 for measuring/monitoring one or more aspects/properties of the tool during workpiece processing (in addition to or instead of sensors in the tool 20).

The tool 20 can process the workpiece 16 by moving the tool insert 24 into the workpiece as the workpiece 16 is rotated by the spindle 18. At the same time, data from at least one sensor 26 in the tool body 22 may be obtained. For example, data relating to at least one of temperature, vibration, load and deflection of the tool may be obtained. Such data may be transmitted to external devices, such as the NC 6 and/or the PC 8, for example, via a wireless link and the interface unit 10. For example, the at least one sensor 26 may communicate with the interface unit 10 via the bluetooth wireless technology standard. In the described embodiment, the data is streamed instantaneously and continuously. However, as will be appreciated, this need not be the case. For example, data may be transmitted at time intervals (regular or irregular) or only when requested, for example. In other exemplary embodiments, the data from the at least one sensor 26 may be stored locally within a memory in the tool 20 and downloaded to the NC 6 and/or PC 8 at a later time, e.g., after tool processing, e.g., via a wired or wireless link.

Fig. 2 shows that a measuring probe 30 can be mounted in the tool holder 12 of the machine tool 4 instead of the tool 20 (fig. 1). In this embodiment, the probe 30 is a contact probe comprising a body 32 mounted to the tool holder 12, a stylus 34 extending from the body 32, and a stylus head 36 at the end of the stylus 34 remote from the body 32. In the depicted embodiment, the stylus 34 may deflect relative to the body 32 (e.g., when the stylus tip 36 contacts a surface), and such deflection may be detected by sensors in the body 32. In particular, in the described embodiment, the probe is a scanning probe (also referred to in the art as an analogue probe) in that the probe 30 can sense and report the degree/amount/degree of deflection of the stylus from a rest position (in contrast to a touch trigger probe, which reports only when the stylus has deflected by, for example, a predetermined threshold amount). Such scanning probes for machine tools are known; for example, having SPRINT available from Renisshaw plc^TMTechnical OSP60 probe. As will be appreciated, other probes and other techniques may be used.

Accordingly, by contacting the stylus tip 36 with the surface of the workpiece 16, the processed portion of the workpiece can be measured. Stylus deflection data from the probe 30 may be streamed instantaneously and continuously (e.g. wirelessly) to the NC 6 and/or PC 8 via the interface 10. According to the tool described above, this can be achieved via a bluetooth connection. As will be appreciated, other techniques may be used to transmit stylus deflection data. For example, data may be transmitted at time intervals (regular or irregular) or only when requested, for example. In other exemplary embodiments, the stylus deflection data may be stored locally within memory in the probe 30 and downloaded at a later time to the NC 6 and/or PC 8, for example via a wired or wireless link.

If desired, data from probe 30 may be combined with machine position data; for example in combination with data regarding the relative positions of the probe 30 and the workpiece 16. For example, data from the probe 30 may be combined with tool holder 12 position data, which may be obtained from encoders (not shown) that monitor the position of the tool holder 12 in any or all of the x, y, and z axes.

Accordingly, as will be appreciated, the measurement data regarding the processed portion of the workpiece may be raw data obtained/output by the probe 30, or may be data obtained by processing raw data obtained/output by the probe 30 (e.g., by combining it with other data such as data regarding the position of the toolholder 12).

As will be appreciated, measurement probes other than scanning stylus deflection probes may be used. For example, a touch trigger measurement probe or a surface finish probe may be used. Alternatively, a non-contact probe may be used. Alternatively, the portion need not be measured on the same machine. For example, the part may be removed from the machine tool and measured on a Coordinate Measuring Machine (CMM) or the like.

Fig. 3 illustrates an exemplary process 100 according to the present invention.

The exemplary process 100 begins at step 102 where the workpiece 16 is processed by the tool 20 and data from at least one sensor 26 of the tool 20 is obtained during workpiece processing. As schematically illustrated in fig. 3, the tool sensor data may be stored in memory (e.g., in PC 8) for subsequent use. As will be appreciated, the data may be stored elsewhere, for example in the NC 6, the interface 10, or elsewhere, such as in network storage or cloud storage.

At step 104, the portion of the workpiece 16 processed by the tool 20 is then measured using the measurement probe 30 to obtain measurement data (e.g., dimensional data and/or surface roughness/waviness data) about the portion. As schematically illustrated in fig. 3, the measurement data may be stored in a memory for later use.

At step 106, the tool sensor data and measurement data obtained at

steps

102 and 104 are used to determine sensor-to-workpiece data calibration information. This can be achieved in a number of different ways. For example, a model may be determined from one or more test cuts and measurements of the workpiece that models the relationship between i) a particular property of the tool (such as the load on the tool, e.g., as measured by a strain gauge) and ii) the dimensional (e.g., hole diameter) error of the portion. Such a model may be in the form of a function or a look-up table, for example. Figure 4a is a graph illustrating a model determined from two different test hole cuts made at two different loads, and from the diameter error of the hole formed by the two test cuts. These results are shown plotted on the graph of fig. 4 a. As shown, a model (e.g., a function) can be determined that fits a straight line through the results of two test cuts. The model may be (or form the basis of) a calibration model of the workpiece. Accordingly, for subsequent cuts of a workpiece (or nominally the same workpiece), hole diameter (and hence actual size of the hole) errors can be inferred from the load measured during the cutting process.

In this example, two test cuts were obtained. However, as will be appreciated, more or fewer test cuts may be obtained. For example, if more than two test cuts are obtained, the calibration model may be a (straight or curved) line based on a best fit of the measurements obtained by the different test cuts.

In an alternative embodiment, the general sensor-to-workpiece data calibration information for the tool (and optionally the machine tool, e.g., for the tool/machine tool combination) may already be obtained. For example, as illustrated by the solid line in fig. 4b, a generic model of the relationship between load and machining error may have been determined for the tool (and optionally the machine tool, e.g. for the tool/machine tool combination). However, the inventors have found that using such a generic model does not necessarily provide accurate measurements of any given workpiece.

Accordingly, the inventors have found that performing one or more test cuts on a workpiece (or on a nominally identical workpiece), measuring the portion(s) being cut, and determining a calibration model/function for that workpiece (and for subsequent workpieces in a series of nominally identical workpieces) can have significant benefits. Accordingly, the sensor-to-workpiece data calibration information may be workpiece specific. This may include, for example, performing a test cut only once, based on which the generic model is adapted. For example, as illustrated in fig. 4b, it may be determined that for the load "x" measured during machining of the hole, the actual error in the diameter of the hole is e2, rather than e1 as predicted by the generic model. This error difference may be assumed to be constant and therefore, as illustrated by the dashed line in the graph of fig. 4b, the adapted calibration model may be determined by offsetting the universal model by the difference between e2 and e 1. As will be appreciated, more than one test cut and measurement thereof may be performed if desired, which may provide more accurate deviation information.

Also, as illustrated in fig. 4c, the same approach can be used for other attributes than load. For example, a generic model of measured vibration and surface roughness (Ra) may be adapted based on actual readings of surface roughness experienced at a particular measured vibration level "y".

The calibration information (e.g., functions, models, data, or other suitable information) may then be stored in memory (e.g., in a PC) for subsequent use.

At some subsequent point in time, the workpiece (or, e.g., a nominally identical workpiece) is again processed by the tool (or, e.g., a nominally identical tool), represented by step 108 in process 100. As illustrated in fig. 3, tool sensor data from at least one sensor 26 of the tool 20 is obtained during workpiece processing and stored in memory (e.g., in a PC) for subsequent use.

At step 110, the calibration information obtained at step 106 and the tool sensor data obtained at step 108 are used to infer measurement data about the portion of the workpiece processed at step 108. For example, in the case of forming a hole, in conjunction with fig. 4a and 4b, this may include using the model determined at step 106 to look up an inferred diameter error based on the load applied to the tool as measured by sensor 26 during the machining process at step 108. Alternatively or additionally, in conjunction with fig. 4c, this may include determining the surface roughness of the portion based on vibrations measured by the sensor 26 during the machining process as at step 108, using the model determined at step 106. Once determined, the inferred measurement data may be stored in memory (e.g., in a PC) for subsequent use, such as step 112. For example, such use of inferred measurement data may include determining at least one of: whether to accept or reject the workpiece; how to adjust subsequent processing of the workpiece in real time or during subsequent processing steps; and/or stop the process.

Accordingly, with the techniques of the present invention, measurement data regarding a processed portion of a workpiece may be determined without actually measuring the portion directly with a measurement tool.

As will be appreciated, rather than extrapolating measurement data of the machined surface, the method may include using the calibration information determined at step 106 to determine process control parameters for controlling subsequent machining steps (of the same or nominally the same workpiece). For example, the method may include determining a threshold vibration level above which corrective action should be taken.

As will be appreciated, references herein to storing data in memory may include storing data in permanent storage and/or temporary memory, such as (random access memory "RAM"). Further, the above-described storing step may be optional. For example, inferred measurement data may be transmitted to an external device and/or used immediately (e.g., by the NC 6 making a decision) without being stored in a storage device.

As will be appreciated, although the NC 6 and the PC 8 are shown to share one interface 10, they may each have their own separate interface 10. Furthermore, such interfaces may be embedded in the NC 6 and/or the PC 8, rather than being separate, as depicted in the figures.

In the above embodiment, the measurement probe 30 is mounted in the tool holder 12 instead of the tool 20. However, as will be appreciated, in alternative embodiments, the measurement probe may be mounted on a separate tool holder or other part of the machine tool. In this case, the tool does not need to be exchanged for a measuring probe.

In the above embodiments, the same part, the same tool, and the same machine are used in all the steps. However, this need not necessarily be the case. For example, the workpiece, tool and/or machine tool used at

steps

102 and 104 may be different (albeit nominally the same) as the workpiece, tool and/or machine tool used at step 108. For example, in one embodiment, calibration information may be obtained on different machines. For example, steps 102 and 104 may be performed on a different machine tool than step 108. In another exemplary embodiment, steps 102 and 108 may be performed on the same machine tool, but step 104 may be obtained on a different device, e.g., a different machine tool or a dedicated measurement device such as a Coordinate Measuring Machine (CMM).

As will be appreciated, in alternative embodiments, tools other than boring bars may be used. For example, the tool may comprise a drill bit, a grinding wheel, or a milling, reaming or milling tool.

As will be appreciated, in alternative embodiments, the relative movement in any or all of the x, y, and z dimensions may be provided by movement of the spindle 18 instead of movement of the tool holder 12, or by movement of the spindle and tool holder. Furthermore, motion may be limited to fewer dimensions, such as only x, and/or y. Furthermore, the described embodiments include cartesian machine tools, however, as will be appreciated, this need not be the case and may be an example of non-cartesian machine tools. Furthermore, as will be appreciated, although the invention is shown in connection with a lathe, the invention may be used with many other types of machine tool equipment and machining centers, such as milling machine equipment (e.g. where the tool is held in a spindle that can be moved). Accordingly, the present invention may be used with embodiments in which the tool is rotated while the part remains stationary.

As will be appreciated, steps 102 and 104 may be repeated, for example, on different (e.g., nominally identical) workpieces, with calibration information being obtained from the workpieces at step 106.

In the above embodiment, the method includes performing an initial test cut and measurement to determine calibration information before subsequent machining occurs. However, as will be appreciated, this need not necessarily be the case, and machining operations to infer information may have been performed prior to determining the calibration information. For example, the method may comprise performing a plurality of machining operations on a workpiece (or nominally workpieces), measuring only one (or only some) of the portions that have been machined (or measuring only one or some of the workpieces, for example) to determine calibration information therefrom, and then using the calibration information to infer information about other portions of the workpiece (or other workpieces) that have been machined.

Claims

1. A method, comprising:

a) causing a tool mounted on a machine tool to process a workpiece, wherein at least one sensor configured to measure one or more aspects of the tool and/or machine tool collects sensor data during the process;

b) the measuring device inspects the portion of the workpiece processed in step a) to obtain measurement data; and

c) and calculating sensor-to-workpiece data calibration information according to the sensor data and the measurement data.

2. The method of claim 1, further comprising inferring information about a workpiece using the sensor-to-workpiece data calibration information and sensor data collected during the processing of the workpiece.

3. The method of claim 1 or 2, wherein the workpiece of step a) is one of a series of nominally identical workpieces to be processed, and wherein, for at least one other workpiece in the series, information about the at least one other workpiece is inferred from the sensor-to-workpiece data calibration information and sensor data obtained during processing thereof.

4. The method of claim 1 or 2, wherein the method comprises:

d) processing the same or nominally the same workpiece using the same or nominally the same tool and the same or nominally the same machine tool as used in step a), an

e) Using the sensor-to-workpiece data calibration information, inferring information about the workpiece from sensor data collected during step d) by the same sensor or nominally the same sensor as used in step a).

5. The method of any of claims 2 to 4, wherein the information about the workpiece inferred from the sensor data comprises measurement data.

6. The method of any of claims 2 to 5, further comprising using the inferred information about the workpiece to adjust subsequent processing of the workpiece or a subsequent nominally identical workpiece.

7. The method of any preceding claim, wherein the sensor data comprises at least one of: vibration, deflection, and/or load.

8. The method of any preceding claim, wherein the measurement data and/or the inferred information comprises at least one of: the position, size, surface roughness, surface waviness of the workpiece.

9. The method of any preceding claim, wherein the processing of the workpiece comprises at least one of: cutting, drilling, grinding, polishing, turning, reaming and milling.

10. The method of any preceding claim, wherein the tool comprises the at least one sensor.

11. The method of claim 10, wherein the tool includes a tool insert and a tool body, the tool insert being mounted to the machine tool apparatus via the tool body, and wherein the tool body includes the at least one sensor.

12. The method of claim 11, wherein the at least one sensor is positioned toward an end of the toolholder proximate the cutting insert.

13. A method according to any preceding claim, wherein step b) is performed by a measuring device mounted on the machine tool.

14. A method according to any preceding claim, wherein the measurement device comprises a measurement probe, such as a contact measurement probe, for measuring a dimensional attribute of the workpiece.

15. The method of any preceding claim, wherein step c) comprises adjusting previously determined sensor-to-workpiece data calibration information based on the sensor data and the measurement data.

16. A method of inferring measurement data relating to a workpiece being processed by a tool mounted on a machine tool, the method comprising, in any suitable order:

a) obtaining sensor data obtained by at least one sensor, the sensor data relating to one or more properties of the tool and/or the machine tool when the workpiece is processed by the tool; and

b) calibrating information to workpiece data using sensors configured for the particular tool in combination with a workpiece and a machine tool, inferring information about the workpiece from the sensor data.